A diffusion sampler of the kind referred to above is disclosed in the technical journal entitled "American Industrial Hygiene Association Journal" (40) July 1979, pages 588 to 591.
The term diffusion sampler is understood to include pure collectors as well as indicating dosimeters.
The known diffusion sampler includes a tubular diffusion vessel which is suitable for collecting gaseous pollutants such as NO, N0.sub.2 or also NO.sub.x and to make the same accessible for subsequent chemical analysis. The tubular vessel of the diffusion sampler is openable at one end and has a permeable lattice carrier at its end lying opposite the opening. The lattice carrier is provided with triethanolamine and is followed by a glass fiber disc impregnated with chromic acid. The NO.sub.x diffusing through the opening and a diffusion zone which follows the opening migrates to the base of the vessel where the NO.sub.2 which is possibly present is held by the triethanolamine on the lattice carrier whereas the NO can diffuse through the lattice carrier and continue until it reaches the glass fiber disc whereat it is oxidized to NO.sub.2 by the chromic acid impregnation and is likewise adsorbed on the triethanolamine layer of the lattice carrier.
The known diffusion sampler includes an air column which contributes a diffusion length through which the pollutants to be collected must pass. A significant disadvantage of this know diffusion sampler is seen in that a ratio between the vessel cross section and the height of the air column must be maintained at least 1 : 3 in order to obtain a reproducible diffusion. The extended length of the dosimeter vessel necessary for this reason makes it inconvenient to handle. In this connection, reference may be had to an article by S. R. Coleman in the technical journal entitled "American Industrial Hygiene Association Journal", 44 (9), page 632, (1983).
Furthermore, a length indicating dosimetry is not possible because the collecting tube would have to be extended still further and this would lead to an undesired enlargement of the diffusion vessel which would make the latter inconvenient to handle.